Effect of specific antibody pretreatment on liver uptake of 111In-labeled anticarcinoembryonic antigen monoclonal antibody in nude mice bearing human colon cancer xenografts

Administration of a large dose (0.2 mg) of unlabeled specific anticarcinoembryonic antigen (anti-CEA) monoclonal antibody (MAB) to nude mice bearing LS174T human colon cancer xenografts significantly decreased normal liver uptake of 111In-labeled anti-CEA MAB (Indacea). Mice bearing tumors of approximately 1 g showed liver accumulation of indium-111 at 48 h following injection of 2 micrograms/10 microCi Indacea of 33.8 +/- 1.5% injected dose per gram (%ID/g) (N = 25). Treatment with 0.2 mg unlabeled anti-CEA MAB reduced this to 8.9 +/- 0.5% ID/g (N = 22; P less than 0.001). The dose of pretreatment was found to be critical. Increasing the amount of unlabeled MAB to 2.0 mg did not significantly improve the liver level of indium-111, but did compromise the tumor uptake of Indacea (15.9 +/- 1.3 versus 12.4 +/- 0.4% ID/g; P less than 0.05). Lowering the dose of pretreatment 10-fold resulted in increased (P less than 0.001) liver uptake of the label (26.5 +/- 2.8% ID/g). The unlabeled anti-CEA MAB treatment given as a single dose or fractionated over several days gave the same results. The decrease in liver uptake was the same for i.v. administration of the unlabeled MAB given 1 week prior to Indacea injection or mixed together with Indacea. With i.p. administration, simultaneous injection of the unlabeled MAB with Indacea was not as effective as pretreatment (20 min to 7 days) in decreasing the liver uptake of 111In (P less than 0.05). Epitope specificity and affinity were shown to be important considerations in the choice of MAB combinations used for pretreatment and imaging. Pretreatment with nonspecific MAB was ineffective in decreasing liver uptake of Indacea.     

The mechanism of hepatic uptake of a radiolabelled monoclonal antibody.

Clinical and experimental scintigraphic studies have found that radiolabelled antibodies are not only taken up by tumour(s) but also by normal liver. The accumulation of radionuclides in this organ poses a major problem to the use of radiolabelled antibodies as diagnostic and therapeutic tools. In an attempt to understand the mechanism of hepatic uptake and clearance of radiolabelled antibodies, the intrahepatic biodistribution of an 111In-labelled MAb (HMFG1), was determined following i.v. administration to normal male rats. Two hours after administration the liver contained 15% of the injected dose, with most of the remaining radioactivity in the blood. The hepatic burden of the 111In MAb remained constant over the next 72 hr in the face of decreasing blood levels of radioactivity as well as its urinary and faecal excretion. At 2 and 72 hr after injection, 50% and 10% respectively of the hepatic radiolabel was due to blood borne antibody. Following a collagenase-cell isolation procedure, only 23% of the amount remaining in the liver at 2 hr was found to be cell-associated; 66% was lost during the cell isolation and purification procedure. Cellular uptake increased with time so that, by 72 hr after administration, 58% was cell-associated and 29% freely removable. At all timepoints, the parenchymal cells contained more activity than non-parenchymal cells. No evidence of antibody-receptor interactions could be obtained either in vivo or in cultures of hepatic parenchymal and non-parenchymal cells. Our data suggest that the bulk of the hepatic burden of 111In MAb results from extravascular pooling of the antibody.     

Effect of tumor size on monoclonal antibody uptake in a metastatic model.

We studied the effect of tumor size on monoclonal antibody (mAb) in a murine hepatic model. Intrasplenic injection of HT-29 LMM metastatic human colon cancer cell line reproducibility results in hepatic metastases formation in congenitally athymic mice. HT-29-15, a murine mAb of the IgG1 class reactive with the HT-29 LMM cell line, and BL-3, an isotype-matched control mAb, were labeled with iodine 125. Labeled mAbs were injected intravenously into mice with hepatic metastases. Animals were sacrificed on day 5, and tumor and normal tissue weighed and counted. Specific mAb uptake (percent injected dose per gram, %ID/g) by hepatic metastases (5.16 +/- 3.96) was significantly greater than nonspecific uptake (1.41 +/- 0.42) (P less than 0.001). %ID/g of tumor was dependent upon the mAb used, and was independent of tumor weight; consequently, a linear correlation between tumor weight and total uptake (%ID) for specific mAb (r = 0.88, P less than 0.0001) and nonspecific mAb (r = 0.99, P less than 0.0001) administration was demonstrated. We have shown both specific and nonspecific mAb uptake per gram of tumor to be a constant for the given mAb/tumor system and with uptake of mAb to be linearly related to tumor weight.     

Radioimmunotherapy of human glioma xenografts in nude mice by indium-111 labelled internalising monoclonal antibody

The potential of 111Indium (111In)-labelled internalising anti-integrin alpha 3 antibody GA17 in the radioimmunotherapy of human glioblastoma xenografts in nude mice was investigated. A radioisotope retention assay showed a rapid release of radioiodine from the glioblastoma cells after the binding of 125I-GA17, whilst 111In-GA17 was retained in the cells for a longer time period. The glioblastoma xenografts showed a high and prolonged uptake of 111In-GA17, and tumour uptake of 125I-GA17 was lower and decreased with time. In the mice which received two injections of 18.5 MBq of 111In-GA17, the growth of the subcutaneous tumour was significantly suppressed compared with the untreated group and mice injected with an 111In-labelled control antibody. These results indicate that GA17 was internalized into the glioblastoma cells and that 111In was retained within the cancer cells. The injection of a high-dose of 111In-GA17 can suppress the growth of tumour xenografts in nude mice.     

The effect of tumor CEA content and tumor size on tissue uptake of indium 111-labeled anti-CEA monoclonal antibody

This study was undertaken to determine the effect of tumor size and tumor carcinoembryonic antigen (CEA) content on the uptake of indium 111 (111In)-labeled anti-CEA monoclonal antibody in nude mice bearing xenografts. The tumor cell lines were WiDr, SW403, and LS174T, human colon cancer derivatives. The murine breast carcinoma cell line EMT-6 was used as a control. Tumor CEA levels (ng/g of tumor +/- standard error of the mean [SEM], measured by enzyme immunoassay (EIA) were: EMT-6, 0; WiDr, 105 +/- 5.7; LS174T, 2052 +/- 198; SW403, 17,575 +/- 1,785. The 111In-labeled monoclonal antibody was injected intravenously into mice bearing a single tumor. At 48 hours postinjection, scintiscan was performed, and the mice were killed so that biodistribution studies could be performed. The uptake of the monoclonal antibody was expressed as percent injected counts per minute per gram of tissue +/- SEM. The non-CEA-producing tumor, EMT-6, showed the lowest tumor uptake (1.4 +/- 0.3). WiDr, an intermediate CEA-producing tumor, showed some tumor uptake (16.4 +/- 1.5). The high CEA-producing tumors, SW403 and LS174T, had high tumor uptake (29.5 +/- 5.0 and 51.1 +/- 6.1, respectively). Biodistribution and scintiscan quality were closely related. Although LS174T had the best tumor uptake, SW403 had the highest CEA tumor content, indicating tumor CEA content cannot entirely predict scintiscan and biodistribution results. Tumor-to-blood (T/B), tumor-to-liver (T/L), and liver-to-blood (L/B) ratios were calculated for each animal and compared with tumor size. It was found that T/L had a negative correlation with tumor size (r = -0.72) and L/B had a positive correlation with tumor size (r = 0.94). These ratios may be useful clinically to follow response to therapy.     

Radioimmunoimaging in malignant melanoma with 111In-labeled monoclonal antibody 96.5

A radiolabeled monoclonal antibody (96.5) reactive with an Mr 97,000 antigen found on over 80% of melanoma cell lines and tissue extracts was examined for its ability to detect malignant melanoma metastases in vivo. For imaging purposes, it was conjugated with diethyltriaminepentaacetic acid and subsequently labeled with 111In by chelation. Thirty-one patients with metastatic melanoma received single injections of monoclonal antibody 96.5 at concentrations ranging from 0.5 to 20 mg and at specific activities of 111In ranging from 0.125 to 4 mCi/mg. Total-body scans were performed at various time intervals following administration. No serious side effects were observed. Of a total of 100 previously documented metastatic sites, 50 imaged for a specificity of 50%. The number of sites imaged increased significantly as the amount of antibody administered increased relative to the average radiation dose. Considerable background uptake of isotope was observed in blood pool and other organs with gradual acquisition of label in tumor sites by 48 to 72 h. Hence, tumor imaging of melanoma using 111In-labeled monoclonal antibody 96.5 appeared feasible, especially at antibody doses above 2 mg.     

Immunoscintigraphy in laryngeal and pharyngeal carcinomas using indium-111 labelled monoclonal antibody

Localization of primary tumors, metastases or recurrences in 13 consecutive patients with histological verification of squamous cell or adenocarcinoma was determined with radioimmunoscintigraphy using monoclonal radiolabelled anti-CEA-antibody. In 12 of the 13 cases, immunohistochemical stainings were positive for CEA. Correct radioimmunoscintigraphic localization was obtained in 15 of the 19 surgically verified tumor sites. There were two positive scintigraphic findings which could not be verified during one year follow-up. The CEA serum concentrations were with one exception normal in all patients, showing that the serum CEA level does not predict the possible benefit from anti-CEA radioimmunoscintigraphy.     

Effect of tumor mass and antigenic nature on the biodistribution of labeled monoclonal antibodies in mice

The effect of tumor mass and antigenic nature on the biodistribution of 111In- and 125I-labeled monoclonal antibodies (MoAbs) was studied using F(ab')2 fragments of three representative anti-tumor MoAbs and SW1116 human colorectal carcinoma grown in nude mice. The 19-9, F33-104 anti-CEA, and 17-1A MoAbs showed specific binding to SW1116 cells. The former two MoAbs recognize circulating CA 19-9 with molecular weights of more than 5,000,000 and CEA of Mr 170,000-180,000, respectively, whereas 17-1A reacts with a nonshedding antigen. Both percentage injected dose per gram tumor and tumor-to-blood ratios were inversely proportional to the tumor mass in nude mice administered 111In- and 125I-labeled 19-9, but liver uptake increased as tumor size increased. Analysis of serum samples and tumor homogenates demonstrated the presence of a high-molecular-weight species, probably due to the antibody binding to CA 19-9. In the case of 111In-labeled anti-CEA MoAb, tumor uptake also decreased and liver uptake increased with tumor size, but this effect was less obvious than that of 19-9. In contrast, tumor and liver uptake of 125I-labeled anti-CEA MoAb, 111In- and 125I-labeled 17-1A and control antibodies were independent of tumor mass. The absolute tumor uptake and tumor-to-blood ratios of all 125I-labeled antibodies were lower than those of the 111In-labeled ones. And the effect of tumor mass was also weaker with 125I-labeled antibodies, probably due to in vivo dehalogenation. These results indicate that the effect of tumor size on the incorporation of labeled MoAb into tumors is dependent on the antigenic nature to be targeted and/or radionuclides used for labeling and that high concentrations of circulating high molecular weight antigens may limit in vivo use of MoAb conjugates.     

Predicted and observed effects of antibody affinity and antigen density on monoclonal antibody uptake in solid tumors.

The uptake and binding of monoclonal antibodies (MAbs) in solid tumors after a bolus i.v. injection are described using a compartmental pharmacokinetic model. The model assumes that MAb permeates into tumor unidirectionally from plasma across capillaries and clears from tumor by interstitial fluid flow and that interstitial antibody-antigen interactions are characterized by the Langmuir isotherm for reversible, saturable binding. Typical values for plasma clearance and tumor capillary permeability of a MAb and for interstitial fluid flow and interstitial volume fraction of a solid tumor were used to simulate the uptake of MAbs at various values of the binding affinity or antigen density for a range of MAb doses. The model indicates that at low doses, an increase in binding affinity may lead to an increase in MAb uptake. On the other hand, at doses approaching saturation of antigen or when uptake is permeation limited, an increase in the binding affinity from moderate to high affinity will have only a small effect on increasing MAb uptake. The model also predicts that an increase in antigen density will greatly increase MAb uptake when uptake is not permeation limited. Our experiments on MAb uptake in melanoma tumors in athymic mice after injection of 20 micrograms MAb (initial plasma concentration, about 120 nM) are consistent with these model-based conclusions. Two MAbs differing in affinity by more than 2 orders of magnitude (3.8 x 10(8) M-1 and 5 x 10(10) M-1) but with similar in vivo antigen densities in M21 melanoma attained similar concentrations in the tumor. Two MAbs of similar affinity but having a 3-fold difference in in vivo antigen density in SK-MEL-2 melanoma showed that the MAb targeted to the more highly expressed antigen attained a higher MAb concentration. We also discuss the model predictions in relation to other experiments reported in the literature. The theoretical and experimental findings suggest that, for high dose applications, efforts to increase MAb uptake in a tumor should emphasize the identification of an abundantly expressed antigen on tumor cells more than the selection of a very high affinity MAb.     

Strategies to enhance monoclonal antibody uptake and distribution in solid tumors

Despite the significant resources dedicated to the development of monoclonal antibody (mAb) therapies for solid tumors, the clinical success, thus far, has been modest. Limited efficacy of mAb in solid tumors likely relates to unique aspects of tumor physiology. Solid tumors have an aberrant vasculature and a dense extracellular matrix that slow both the convective and diffusive transport of mAbs into and within tumors. For mAbs that are directed against cellular antigens, high antigen expression and rapid antigen turnover can result in perivascular cells binding to and eliminating a significant amount of extravasated mAb, limiting mAb distribution to portions of the tumor that are distant from functional vessels. Many preclinical investigations have reported strategies to improve mAb uptake and distribution; however, to our knowledge, none have translated into the clinic. Here, we provide an overview of several barriers in solid tumors that limit mAb uptake and distribution and discuss approaches that have been utilized to overcome these barriers in preclinical studies.     

Biodistribution of indium-111-labeled OC 125 monoclonal antibody after intraperitoneal injection in nude mice intraperitoneally grafted with ovarian carcinoma

The purpose of this work was to study the biodistribution of 111In-labeled OC 125 monoclonal antibody (MAb) with known affinity for ovarian carcinomas in a nude mouse model grafted i.p. with a human ovarian cancer (NIH:OVCAR-3). Tumor uptake 24 h after i.p. injection was higher with intact 111In-labeled OC 125 MAb (28 +/- 7.44%ID/g) than with 111In-nonspecific immunoglobulin (6.86 +/- 1.35%ID/g). The kinetics of tumor uptake also differed, showing a plateau followed by a drop at Day 7 with 111In-OC 125 MAb and a decrease beginning at 24 h with 111In-nonspecific immunoglobulin. Tumor-to-normal tissue ratios ranged between 29.91 +/- 11.85 and 0.68 +/- 0.15 with 111In-OC 125 MAb and between 4.50 +/- 1.06 and 0.53 +/- 0.04 with 111In-nonspecific immunoglobulin according to the normal tissues and the time points considered. Tumor uptake 2 h after injection was the same for F(ab')2 fragments as for intact MAb, whereas maximum uptake at 24 h (18.76 +/- 4.62%ID/g) was lower and was followed by a decrease at Day 4. Tumor-to-normal tissue ratios were in the same range, except for the tumor to blood ratio which was higher and the tumor to kidney ratio which was lower at 24 and 96 h. Maximum tumor uptake was higher after i.p. (30.77 +/- 4.76%ID/g) than i.v. (14.59 +/- 2.70%ID/g) injection. Instead of attaining the plateau noted after i.p. injection, tumor uptake after i.v. injection remained low at 2 h (2.11 +/- 1.66%ID/g), reaching its peak only after 96 h. 131I-OC 125 injected i.p., which reached maximum tumor uptake at 2 h (13.53 +/- 4.25%ID/g), showed tumor-to-tissue ratios ranging between 15.98 +/- 2.63 and 0.96 +/- 0.86, i.e., not very different from those with 111In. After i.p. injection of a radiolabeled colloid solution, maximum tumor uptake was reached at 96 h (20.22 +/- 5.35%ID/g), but with very high nonspecific uptake in liver (31.06 +/- 6.22%ID/g) and spleen (55.23 +/- 14.11%ID/g). These results indicate high, selective tumor uptake of 111In-OC 125 after i.p. injection and demonstrate the feasibility of i.p. radioimmunotherapy of ovarian carcinomas.     

Kinetic model for the biodistribution of an 111In-labeled monoclonal antibody in humans

Using data from 12 patients, we have analyzed the pharmacokinetics of 111In-9.2.27, an antimelanoma monoclonal antibody, following i.v. infusion. Plasma data and scintillation camera images obtained from patients receiving either 1, 50, or 100 mg of monoclonal antibody indicated dose-dependent (i.e., saturable) kinetics. Based on these observations and known immunoglobulin kinetics, we developed a nonlinear compartmental model to describe the biodistribution of 111In-9.2.27 and the other coinjected 111In-associated compounds. The model included (a) three compartments representing intact 111In-9.2.27 ("plasma," "nonsaturable," and "saturable binding" compartments), (b) four compartments representing 111In-diethylenetriaminepentaacetic acid, and (c) one compartment representing 111In in an undetermined chemical form ("extravascular delay" compartment). Analysis of the rate of urinary excretion relative to plasma concentration indicated that the saturable binding compartment was a site for catabolism of monoclonal antibody. Further examination of the urinary data, together with previous studies of the site(s) of immunoglobulin catabolism, suggested that additional elimination took place from either the plasma or the nonsaturable compartment. The model indicated that to fill the saturable sites would require a dose of approximately 0.5 mg and suggested that greater than 3.5 mg would maintain saturation for 200 h. Computer integration of gamma camera counts over the spleen revealed a clear saturable component of uptake, whereas integration over the liver showed no such pattern. The proposed model was fitted to the liver and spleen imaging data by summing fractions of model simulations of each compartment. That analysis confirmed the suspected saturable uptake by the spleen (21% of the saturable binding compartment) and revealed a quantitatively important component of saturation in the liver (35% of the saturable binding compartment) that was not obvious from initial examination of the images. When the results were expressed on a concentration basis, the spleen accounted for 247% of the saturable compartment per kg, whereas the liver accounted for 25%/kg. The bone marrow also showed saturable uptake; hence, the saturable uptake may relate to the sinusoidal blood supply characteristic of liver, spleen, and marrow. The model predicts the dose levels required to overcome saturable background, suggests appropriate doses and schedules for cold loading strategies, and provides a format for explicit inclusion of tumor antigen.     

Enhancement of monoclonal antibody uptake in human colon tumor xenografts following irradiation

Indium-111-labeled AUA1 tumor-associated monoclonal antibody raised against an antigen of colon adenocarcinoma was used to evaluate the effect of ionizing radiation on antibody uptake by the LoVo adenocarcinoma cell line grown as a xenograft in nude mice. Tumors were exposed to single doses of external X-irradiation of between 400 and 1600 cGy followed, 24 h later, by administration of specific or nonspecific antibody. Animals were sacrificed 3 days after antibody administration. At doses higher than 400 cGy, tumor uptake with both specific and nonspecific antibody was significantly increased. No difference in changes in tumor volume was observed between the groups receiving irradiation and the controls. Specific antibody uptake by tumors was always significantly higher than nonspecific having an approximate 4-fold binding advantage. Vascular permeability and the vascular volume of irradiated and control tumors was measured 24 and 72 h after irradiation, using iodine-125-labeled nonspecific antibody and labelling of the red blood cells in vivo with 99mTcO4. At doses higher than 400 cGy, vascular permeability in the tumor 24 h after irradiation was significantly increased (P less than 0.05), while the vascular volume decreased (P less than 0.001) compared to control values. However at 72 h after irradiation there was no difference between treated and control groups. The results obtained in this study suggest a potential value of external irradiation to increase monoclonal antibody uptake by tumors governed mainly by the increased vascular permeability of the tumor vasculature soon after the irradiation exposure.     

131I-G250McAb治疗荷人肾透明细胞癌裸鼠的实验研究

目的:研究131I标记的抗肾癌相关抗原G250单克隆抗体(131I-G250McAb)在荷人肾透明细胞癌裸鼠体内的分布,探讨应用131I-G250单克隆抗体治疗实验性人肾癌的可行性和有效性.方法:将标记好的131I-G250单克隆抗体1 mL/只(3.7 MBq)静脉注射荷人肾癌裸鼠体内,后分批处死裸鼠,测定每克组织摄...     

Pharmacokinetics of 111In-labeled anti-p97 monoclonal antibody in patients with metastatic malignant melanoma

Twenty-eight patients with metastatic malignant melanoma received anti-p97 murine monoclonal antibody (96.5) infused over 2 h at doses between 1 and 20 mg coupled to either 2.5 or 5.0 mCi of 111In by the bifunctional chelating agent diethyltriaminepentaacetic acid. Clearance of 111In from plasma closely fit an open, one-compartment mathematical model (r2 greater than 0.90). The overall half-life of 111In plasma was approximately 31 h and did not appear to be dependent on the total dose of antibody administered. The apparent volume of distribution of the 111In label approximated the total blood volume (7.8 +/- 0.7 liters) at the 1-mg dose and decreased to 3.0 +/- 0.14 liters at the 20-mg dose, suggesting saturation of antigenic or other extravascular binding sites at higher antibody doses. The clearance of the murine monoclonal antibody itself from plasma was measured by an enzyme-linked immunosorbent assay. The pharmacokinetics for the murine antibody in plasma also fit an open, one-compartment mathematical model. All pharmacokinetic parameters for unlabeled antibody closely paralleled those found for 111In-labeled antibody pharmacokinetics. This suggests that the 111In radiolabel remains complexed to the monoclonal antibody after in vivo administration. The cumulative urinary excretion of the 111In label over 48 h was between 12 and 23% of the total administered dose and is assumed to represent 111In-labeled chelate complex unattached to antibody. Analysis of the 111In label in spleen, liver, heart, and kidney showed that the concentration of label in liver tissue was reduced with increasing antibody doses and coincided with changes in the apparent volume of distribution. These studies show that murine monoclonal antibodies are cleared slowly from the circulation in humans and that early, rapid distribution of labeled antibody to the liver can be reduced by increasing the dose of unlabeled antibody. This may be particularly important in limiting hepatic toxicity when administering antibody coupled to drugs, radionuclides, or toxins.     

Intravesical administration of indium-111-labelled hmfg2 monoclonal antibody in superficial bladder carcinomas

Tumour-associated HMFG2 monoclonal antibody (MAb) was labelled with indium-111 and administered intravesically to 20 patients with known or suspected superficial bladder carcinoma. The antibody solution was kept in the bladder for 1 hr and was then washed out. Cystoscopy was performed at 2 and 24 hr after instillation. Radioactivity of tumour and normal tissue obtained from the bladder during cystoscopy and cells recovered from urine after the instillation were counted in a gamma-counter. Conventional histology, immunocytochemistry and autoradiography were also performed. Mean uptake at 2 and at 24 hr was higher in tumours than in normal samples. Autoradiography showed selective accumulation of radioactivity in cells which expressed the antigen detected by the HMFG2 MAb. There was no correlation of tumour uptake with the grade of tumour. No radioactivity was found in the blood of patients after the instillation. Based on dosimetric calculations, however, the radiation dose that can be delivered to the tumours is not sufficient to be cytotoxic, possibly due to inadequate penetration and retention by tumour tissue. Nevertheless, the significant difference between antibody uptake by the tumours and that by normal urothelium, observed in our study, allow for the possibility of using this approach therapeutically.     

Interferon-induced changes in pharmacokinetics and tumor uptake of 111In-labeled antimelanoma antibody 96.5 in melanoma patients

The type I interferons [both partially purified human leukocyte interferon (HuIFN-alpha) and recombinant alpha interferon] and the type II interferons have been shown to increase the expression of tumor-associated antigens in vitro. To determine whether HuIFN-alpha could increase tumor acquisition of the antimelanoma antibody 96.5 in vivo, five patients with metastatic malignant melanoma were treated with HuIFN-alpha at a dose of 3 X 10(6) units daily by im administration. Twenty-four hours after the first dose of HuIFN-alpha, 1 mg of antibody 96.5 labeled with 5 mCi of 111In was coadministered with 19 mg of unlabeled 96.5. Five patients matched for metastatic site and lesion size who had not received HuIFN-alpha were also given a dose of 5 mCi of radiolabeled 96.5 at the same total antibody dose (20 mg). In patients treated with HuIFN-alpha, there was a statistically significant increase in the plasma half-life of the 111In label (39.7 +/- 3.3 hr) compared to the untreated control group (29.8 +/- 3.2 hr). In addition, there was an increase in the apparent volume of distribution of the antibody in the HuIFN-alpha group (5.56 +/- 0.67 L) compared to controls (3.15 +/- 0.5 L) suggesting both an increased immediate extravascular distribution of radiolabeled antibody and a decrease in the subsequent rate of clearance of antibody from plasma. These two phenomena result in a 28% decrease in the area under the concentration curve in the HuIFN-alpha-treated group compared to controls. Computer analysis of whole-body scans from patients showed a threefold increase in radiolabeled antibody distributed to tumor relative to blood pool but no change in organ:blood ratios for liver, spleen, bone, or kidney compared to controls. This pilot study suggests that treatment of patients with HuIFN-alpha results in an improved distribution of radiolabeled antibody to tumor target without a concomitant increase of label in normal nontarget tissues. In addition, this change in whole-body distribution of antibody is manifested by changes in the pharmacokinetic parameters measured for monoclonal antibody.     

Specific radioimmunotherapy using 90Y-labeled monoclonal antibody in erythroleukemic mice

Radioimmunotherapy using 90Y-labeled diethylenetriamine pentaacetic acid-antibody conjugates was studied in Rauscher erythroleukemia virus-infected mice. Preliminary experiments showed that biodistribution profiles for nonrelevant mouse monoclonal antibody and polyclonal bovine immunoglobulin were identical in both normal and leukemic mice. Therefore, bovine immunoglobulin G was selected as the control immunoglobulin in order to permit comparison to current clinical trials of radioimmunotherapy regimens. Specific monoclonal antibody was two- to three-fold more potent than bovine immunoglobulin G in therapy, as assessed by reduction of splenomegaly (dose required for half-maximal effect, 9 microCi versus 16 to 27 microCi). Mice treated with 50 microCi 90Y-labeled control immunoglobulin had spleens which were twice the normal size and showed extensive areas of erythropoiesis indicative of the presence of tumor foci; in contrast, doses as low as 27 microCi 90Y-labeled specific antibody resulted in complete remission with no microscopic evidence of tumor foci in either spleen or liver. Although reversible marrow toxicity was observed it was not dose limiting. These results demonstrate that tumor-specific therapy is possible using 90Y-labeled antibody.     

Immunoscintigraphy and pharmacokinetics of indium-111-labeled ZME-018 monoclonal antibody in patients with malignant melanoma

Immunoscintigraphic and pharmacokinetic characteristics of 111In-labeled ZME-018 monoclonal antibody were examined in 8 patients with malignant melanoma. Each patient received a single intravenous infusion of 20 mg of ZME-018, coupled to 3 mCi of 111In without any acute toxicity. Scintigrams were taken 1, 3, and 6 days after the administration, and blood and urine samples were also taken frequently. Rapid clearance of some radioactivity was seen in early urine samples in the form of 111In DTPA, but after 1 day, urinary excretion of radioactivity was slow and steady, with an average of 2.5% of the injected dose excreted per day. The scans demonstrated that there was blood retention of radioactivity in the heart and great vessels 1 day after infusion and considerable clearance from the blood pool occurred by 3 days. However, 111In was deposited in the liver, spleen and bone for up to 6 days. The optimal time for imaging appeared to be at 3 days. Nineteen out of 26 known lesions or 6 out of 8 patients were positive. There were 21 lesions detected that were not suspected during the work-up the patient. Five patients developed human anti-mouse antibody in the serum by 3 weeks. These results suggest that immunoscintigraphy with 111In-labeled ZME-018 antibody is safe and useful for the detection of metastatic lesions in a selected group of patients with malignant melanoma.     

Immunospecific saturable clearance mechanisms for indium-111-labeled anti-melanoma monoclonal antibody 96.5 in humans

Liver uptake of 111In-labeled monoclonal antibodies (MoAb) remains a significant problem in radioimaging studies to date. To determine if the observed liver uptake of an 111In-labeled anti-melanoma antibody 96.5 (111In-96.5) was dependent on the presence of hepatic antigen or on recognition of circulating murine antibody, escalating doses of an unlabeled nonimmunoreactive MoAb (NIR-MoAb) were administered to 18 patients with metastatic malignant melanoma either 1 or 24 h prior to an infusion of 1 mg of 111In-96.5. The number of metastases imaged, pharmacokinetics, and the ratio of radioactivity (expressed as average counts/pixel) in liver (L), spleen (S), bone (B), and kidney (K) compared to blood pool (heart = H) were examined. Results were prospectively compared with data from six patients who received immunoreactive unlabeled 96.5 prior to 111In-96.5. Increasing dose or changes in the preinfusion time of NIR-MoAb had no significant effect on the biodistribution of 111In-96.5. In contrast, patients who received unlabeled, immunoreactive 96.5 prior to 111In-96.5 infusion demonstrated a significant drop [P less than 0.001] in the liver/heart ratio of radioactivity [2.81 +/- 0.35 (SEM)] compared to patients receiving the identical dose of NIR-MoAb [10.35 +/- 1.33]. Significant decreases in spleen/heart and bone/heart ratios were also observed. Pharmacokinetic studies showed that the volume of distribution (Vd) and the plasma t1/2 both decreased when 96.5 was administered compared to NIR-MoAb. In addition, a 4-fold increase in concentration X time was obtained after 96.5 antibody was administered compared to NIR-MoAb. More metastases were imaged in patients receiving preinfusions of 96.5 (23 of 28) than in patients receiving NIR-MoAb (10 of 18; P less than 0.05). Although tissue distribution of 111In-labeled antibody can be ascribed to nonspecific organ clearance of murine antibodies, a substantial component of tissue disposition of antibody 96.5 was shown to be a consequence of specific clearance of immunoreactive antibody which may cross-react with tissue antigens.